The present invention relates to a two-piece type optical imaging lens, especially to an optical imaging lens for mobile phones or image sensors such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) formed by a two piece of lens with features of high performance, minimized total length and low cost.
Along with advanced technology, electronics become more compact and multifunctional. Besides digital still cameras, PC (personal computer) cameras, network cameras and mobile phones, even personal digital assistants are equipped with image pick-up devices such as imaging lens. For meeting requirements of easy-carrying and humanization design, the image pick-up device not only need to have good imaging quality but also need to have compact volume and lower cost so as to extend applications thereof. Especially for applications on mobile phones, the requirements above mentioned are much more important.
There are various materials available for producing conventional spherical ground glass lens. Moreover, the spherical ground glass lens is better for correcting chromatic aberration so that it is adapted widely. Yet it's difficult to correct aberrations such as spherical aberration or astigmatism for the spherical ground glass lens with smaller F Number and larger field angle. In order to improve above shortcomings of conventional spherical ground glass lens, aspherical plastic lens or aspherical molded glass lens is applied to the image pick-up devices available now so as to obtain better imaging quality. For example, refer to the lenses disclosed in U.S. Pat. No. 6,813,095, optical image pick-up lens, U.S. Pat. No. 6,031,670, wide-angle lens or Japanese patent P2001-183578A, imaging lens etc.
However, the total length of the above image capturing devices is still too long. For example, in the lens set disclosed in Japanese patent P2001-183578A, imaging lens, the distance d between a first surface of the first lens element and a second surface of the second lens element is no less than 0.9f (d≧0.9f, f is an effective focal length of an optical lens assembly according to the present invention) so that the volume of the lens can't be reduced. Neither does the cost. Such kind of design can't satisfy compact and light requirements of electronics. Furthermore, applications of such lens are limited severely, especially on mobile phones.